Abstract

A short first metatarsal can lead to transfer metatarsalgia of the second and third metatarsal heads and is unsightly. Many people elect to undergo a lengthening procedure, but metatarsal lengthening for brachymetatarsia is a deceptively simple operation. Surgery can lead to stiffness or subluxation of the MP joint, deformity of the metatarsal, or nonunion at the lengthening site. This case will review a method for salvage of a failed lengthening of the first metatarsal.

Brief Clinical History:

This is a 25 year old woman who underwent lengthening of her first metatarsal for brachymetatarsia. The lengthening procedure resulted in poor regenerate formation and deep infection of the lengthening site. The infected regenerate was debrided and an antibiotic bead placed in to the wound. The patient presented with a medial draining sinus still wearing the external fixator.

Preoperative Clinical Photos:

Preoperative Problem List

Nonunion of the first MT with a bone defect

Previous infection of the regenerate

Unstable fixation

Post traumatic arthritis of the first MP joint

Treatment Strategy

A staged treatment approach was utilized:

The external fixator was removed, the nonunion site was debrided through the draining medial incision, cultures were taken, and a large antibiotic PMMA bead was placed into the defect.

A bicortical iliac crest bone grafting was performed once the wound closed and there were no signs of infection. A stable external fixator was placed spanning the defect site and an axial wire was added for stability.

Basic Principles

The basic principles for the treatment of an infected nonunion apply to this situation: eradicate the infection with debridement and local and systemic antibiotics, autologous bone grafting v bone transport to fill the defect, stable fixation to allow union. The preservation of length was an important goal in this case. The patient had already sacrificed much effort towards obtaining a longer metatarsal and wanted to maintain that length. Another option was to shorten the metatarsal back to the pre-lengthening position and compress until union.

Images During Treatment:

Figures 4: The first stage of the reconstruction is compete with the antibiotic cement spacer and provisional fixation noted.

Figures 5: This x-ray shows the bi-cortical structural iliac crest autograft filling the defect with an axial alignment pin and a medially based external fixator. The first MP joint was essentially auto-fused at the time of initial presentation. Therefore the joint was compressed along with the graft.

Figures 6: There is symmetry of the feet with preservation of the newly gained length of the first metatarsal.

Technical Pearls:

The mini-external fixator can be applied dorsally or medially to the metatarsal. The revision external fixator pins were placed from the medial side in order to avoid the previous loose pin sites that were placed dorsally. The most proximal pin was advanced into the second metatarsal in order to further improve the purchase and stability of the frame.

If the first MP joint were viable then an additional set of pins would be placed in order to distract the first MP joint.

The axial pin prevents dislodging of the graft during compression of the fixator.

Outcome clinical photos and radiographs:

Avoiding and Managing Problems

The placement of half pins directly into the autograft should be avoided both for fear of infection and for fear of compromising the structural strength of the graft.

Pin purchase and fixation in general in the metatarsal is less than ideal. This makes pin loosening a real problem. The best way to avoid loosening is protective weight bearing during the entire healing period. The orientation of the metatarsal transverse to the ground imparts a bending moment to the bone upon weight bearing. This is unlike the tibia and femur with their vertical orientation. This further supports the need for minimal weight bearing during the healing phase of the bone graft incorporation.

I strongly believe in autograft for this procedure. Allograft will have a more difficult time healing and is subject to stress fracture with time.